1. Field of the Invention
This invention relates to liquid sample collector interface used for collecting samples in dissolution testing apparatuses and, in particular, to liquid sample collector interface in the form of cannulas with high capacity filters and improved housing.
2. Description of Related Art
Drugs are commonly manufactured in the form of pills, which are disseminated into the body over a period as the pill dissolves. Manufacturers of pills are required by law to determine the precise dissolving characteristics of a pill before it is placed on the market. In the pharmaceutical industry, the stirring or agitation of sample drugs or other substances in test vessels is an important step in mimicking the dissolution rate or dissolution characteristics of a drug within the stomach. Examples of such test procedures include those performed for the purpose of testing and analyzing the rate at which doses of a drug is released from pharmaceutical products, such as tablets or capsules, under controlled conditions. The procedural steps, test duration, dissolution medium, and apparatus employed in dissolution tests typically must comply with established, well-recognized guidelines, such as those promulgated by United States Pharmacopeia (USP), in order for the test to be accepted as valid for the specific substance tested. The apparatus utilized for carrying out dissolution testing typically includes a vessel plate having an array of apertures into which test vessels are mounted.
Each test vessel includes a liquid called media, which is a dissolution bath that essentially duplicates the liquid solution that is contained within the stomach, with a precise quantity of the solution placed within the test vessel. The pill or capsule to be tested is then inserted within the test vessel with a mixing paddle inserted therein the test vessel to mix the solution at a precise rate, which duplicates the natural turbulence (churning) that is created within the stomach. Aliquots are then removed from the solution at precise time intervals, which are then analyzed to determine the amount of drug that has been dissolved within the solution in relation to the time that the pill or capsule has been in the solution.
In general, the removal of aliquots (dissolution samples) may be accomplished by cannulas of the type illustrated in the prior art FIG. 1A, which are known as resident cannulas. They are called resident cannulas because a stainless steel hypodermic tubing 102 portion of the resident cannula 100 resides within the media (dissolution bath) throughout a dissolution test period. As illustrated, the resident cannula 100 is comprised of the stainless steel hypodermic tubing 102, which is press fitted into an exterior of a housing 106 of the cannula 100. As best illustrated in FIG. 1B, the housing 106 includes an enclosure or cap 104 that has a cylindrical outer perimeter that frictional secures within the commensurately configured housing 106 by an O-ring washer 108, which also seals the cap 104 within the housing 106. As best illustrated in FIG. 1C, the housing 106 has a hallow cylindrical interior 110, with an aperture 112 that communicates with an end of the press-fitted stainless steel hypodermic tubing 102. As illustrated, the bottom surface of the interior 110 of the housing 106, surrounding the aperture 112 is concaved, creating a holding area 114 for the media drawn, which prevents a disc configured filter 110 from blocking the aperture 112 when the cap 104 is assembled and secured within the housing 106.
As illustrated in FIG. 1D to 1G, the cap 104 includes a port 120 at the exterior side of the cap 104 with an aperture 116. The port 120 is generally coupled to a collection mechanism such as a pump, with the pump creating a vacuum to draw aliquots (dissolution samples) from the media through the stainless steel hypodermic tubing 102, the aperture 112 of the housing 106, and then the cap 104 via filter 110, the aperture 116, and the port 120 for testing. As illustrated in FIG. 1E, the cap 104 includes the disc shaped filter 110 housed within a cylindrical filter chamber 118, with the filter 110 removing possible “debris” from the media prior to removal and analysis thereof.
Regrettably, most prior art cannulas 100 suffer from obvious disadvantages in that the prior art uses a small capacity disc filter element 110 that may clog prematurely after passing only a small sample volume. This is critical for methods that require multiple sample time points or large sample volumes that are often the case with UV analysis. In addition, automated sampling systems commonly require several milliters of wash volume to eliminate carryover, which quickly clog the filters 110. Another obvious disadvantage is that the filter disc 110 is installed flush with the end 140 of the cap 104 (FIG. 1E) and can only be removed with a tool 122 as illustrated in FIG. 1F. A further obvious disadvantage of the prior art cannulas is that the original design incorporates the filter cap 104 that is retained by a friction fit O-ring 108. The friction fitting is not sufficiently strong to handle the high pressure that is likely to occur during back washing. That is, the cap 104 will most likely pop-out of the housing 106 during the process. Back washing is a desirable method of extending the life of the filter element 110. Most auto-sampling systems may be programmed to perform backwashing.
Reference is made to the following few exemplary U.S. Patent Publications, including U.S. Pat. Nos. 5,639,953; 5,639,974; 5,682,001; 5,816,701; 6,006,777; 6,076,410; 6,170,980; 6,422,098; D377,152; D424,458; 2002/0119076.
Accordingly, in light of the current state of the art and the drawbacks to current resident cannulas mentioned above, a need exists for a liquid sample collector interface that would use a filter with a larger surface area (higher capacity fitter), that the filter would be replaced without using any tools, and that would have a cap and housing coupling that would withstand back washing pressures.